As means for supplying fuel in an atomized state to combustion chambers in an internal combustion engine such as a diesel engine, fuel injection nozzles are generally used. Such fuel injection nozzles have had a construction wherein a conical pressure-receiving surface is formed at the tip end of a needle valve axially slidably received inside a nozzle body and the needle valve is opened by a fuel pressure being made to act on this pressure-receiving surface whereupon fuel is injected into a combustion chamber of the engine through a plurality of nozzle holes formed in the tip of the nozzle body.
However, with this construction, the fuel injection pressure, the injected amount and the injection speed are generally determined by a fuel injection pump, and furthermore it is not possible to increase or decrease the total nozzle hole area. Consequently, during low-speed running of the engine the fuel injection pressure decreases and during low-load running of the engine the injection time becomes short and thus it is not possible to maintain a good combustion state, and consequently it has been difficult to promote fuel combustion and achieve improvements in output and fuel consumption and reductions in combustion noise and NOx emissions.
As means to overcome this, in Japanese Unexamined Patent Publication No. S.59-180063, a fuel injection nozzle whose total nozzle hole area is variable was proposed. In this related art, a plurality of nozzle holes (upper nozzle holes) are formed spaced in the circumferential in a wall enclosing the tip part of the nozzle body, and another plurality of nozzle holes (lower nozzle holes) are formed spaced in the circumferential direction in the same wall at a level below the upper nozzle holes in the axial direction of the nozzle. A shaft passes axially slidably through a through hole formed down the center axis of a needle valve received in the nozzle body with the circumferential surface of the tip of this shaft positioned so that it covers the lower nozzle holes, and by this shaft being moved in the axial direction by an actuator the lower nozzle holes can be opened.
However, in this related art, because it is not the degree of opening of each of the nozzle holes that is changed but rather it is merely the number of open nozzle holes that is changed, there have been the problems that it is not possible to carry out fine adjustment based on the running state of the engine and that the spray direction of injections changes with the selection of the nozzle holes.
In Japanese Unexamined Patent Publication No. H.4-76266, another fuel injection nozzle whose total nozzle hole area is variable is proposed. This related art fuel injection nozzle is of a rotary valve type. Specifically, a well is formed in the tip part of a nozzle body and a plurality of nozzle holes (eight) connecting with the well are formed spaced in the circumferential direction in a wall enclosing the well. A rotary shaft passes through a through hole formed axially down the center of the needle valve, a tip portion of this rotary shaft is positioned in the well, and a plurality of channels (four) which connect a fuel pressure chamber inside the well to the nozzle holes when the needle valve opens are provided in the rotary shaft. By rotation of this rotary shaft, the number of open nozzle holes is switched between eight and four,
However, in this related art also, it is just the number of open nozzle holes that is varied, and there are the problems that it is not possible to carry out fine adjustment based on the running state of the engine and that the spray direction of injections changes with the selection of the nozzle holes. Also, the wall forming the well forms a straight cylinder parallel with the nozzle axis, and the rotary shaft serving as the rotary valve is also cylindrical. Because of this it has been difficult to fix the position of the rotary shaft constituting the rotary valve during fuel injection. That is, even when the nozzle holes have been adjusted to a required degree of opening by the angle of the rotary shaft being changed the rotary shaft easily slips undesirably in its direction of rotation about its axis when a high fuel injection pressure acts at the nozzle holes. Consequently, it has not been possible to avoid the positional relationship between the nozzle holes and the channels slipping and the nozzle hole area becoming larger or smaller than the set size.
For these reasons, in both of these related art examples there has been the problem that it is difficult to accurately carry out fine control of the total nozzle hole area in accordance with the load and speed of the engine.
Also, to realize optimal fuel combustion of the engine, it is desirable to control the injection rate so as to conduct a pilot injection before a main injection. To this end it is necessary to create a state, between a pilot injection at a low injection rate and a main injection, wherein injection is not carried out, and to do this it is necessary structurally to be able to intentionally allow leakage of fuel to a low pressure side while the needle valve is open. However, in the former of the related art nozzles described above, because the upper nozzle holes are always connected with the combustion chamber, it is not possible to create a non-injection state. And also in the latter of the related art examples described above, because a plurality of nozzle holes are always connected with the combustion chamber, it is not possible to create a non-injection state. Furthermore, because the contact between the outside of the rotary shaft serving as the rotary valve and the inside wall of the through hole of the needle valve forms a seal, for this reason also it is not possible to provide a non-injection state. Therefore, it has been impossible to conduct a pilot injection.
With regard to pilot injections, a control mechanism in a jerk type fuel injection system is proposed in Japanese Unexamined Patent Publication No. H.7-77124. However, in this related art, because the injection amount and the injection period and so on of the pilot injection are determined by the relative positions of a plunger and a leak hole of a fuel injection pump, there has been the problem that the degree of freedom of these parameters is small.
In Japanese Unexamined Patent Publication No. H.7-54370, a solenoid-driven fuel injection nozzle is proposed, but in this related art there is the problem that it is not possible to apply an optimal nozzle hole area to a pilot injection.